With the increasing trend of unmanned aerial vehi-cles (UAVs) applications, UAV-based base station (BS) has gained significant popularity for rapid deployable networks. Compared with the fixed infrastructure that could be severally disrupted in the case of natural disasters, the UAV-based BSs are easily for deployment and can provide the emergency communication in the target areas. In addition, for the limited power supply in UAV, energy-efficient transmission is also essential in the wireless coverage. Accordingly, in this paper we focus our attention on
the maximization of the coverage for UAV-based BS under the constraint of the transmitting power. By modeling the wireless channel in low altitude and setting up the relationship between the antenna beam angle and antenna gain, we formulate the energy-efficient coverage problem as the 2-dimensional optimiza-tion equation respected to the flight altitude and beam angle. In this way, according to the transmitting power allocation(adjusting the antenna beam angle) and UAV deployment (setting the suitable flight altitude), we can maximize the coverage area
with the limited power supply. The simulation results also verify the effectiveness of the optimization.